Studies done under controlled environment conditions have confirmed the field studies done by Chaudhuri et al. (1990), Kirkham et al. (1992), Nie et al. (1992a), and Wall et al. (2006). Kaddour and Fuller (2004) grew three Syrian cultivars of durum wheat (T durum Desf.) under controlled environmental conditions with either 400 |imol/mol CO2 or 1000 |imol/mol CO2 at two levels of water availability. Plants grew in a loam-based compost. The fully irrigated pots were given water to reestablish 90% of available water content (about pot capacity) once the soil water availability had reached 60% available water capacity. Water in the pots in the drought-stressed treatment was restored to 70% available water capacity when the soil water availability had reached 45% available water content. All cultivars responded in a similar manner to both the CO2 and water stress. Raising the CO2 level enabled plants to compensate for the low water availability, so that plants at high CO2 with drought stress had the same ear number as those under ambient CO2 and irrigated conditions (Figure 1.11). Leaf area index at ear emergence was depressed by low water availability but was unaffected by CO2 level (Figure 1.12). Biomass production followed the same pattern as for ear number, with CO2 improving dry weight under both water-stressed and irrigated treatments (Figure 1.13).
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